The postnatal development of adrenergic mechanisms is being studied in piglets under pentobarbital anesthesia. Work in progress comprises analysis of cardiovascular responses to electrical stimulation of efferent sympathetic nerves to the hindlimb; the presence of a cholinergic component of these responses under study include heart rate, arterial pressure and regional blood flows (femoral, cephalic, renal) and utilize strain gauge pressure transducers and electromagnetic flowmeter recordings. The proposed research will complete experiments on the femoral, circulation, extend the investigation to include similar experiments on the mesenteric artery circulation, and initiate a study of blood flow redistribution among femoral, renal and mesenteric circulations during physiologic stress. The presence of adrenergic and cholinergic mechanisms in the femoral and mesenteric circulations will be assessed from effects of efferent sympathetic nerve stimulation and intra-arterial injections of norepinephrine and acetylcholine before and after receptor blockade in intact animals of different age groups. The existence of age-dependency for any differences in magnitude of blood flow and resistance changes will be determined statistically. Control experiments will include sham operations and observations in mature miniature swine. This research is expected to provide knowledge about the role of peripheral vascular mechanisms in the autonomic regulation of cardiovascular function in the neonate.